Monday, March 12, 2012

Thoughts on the Sendai, Japan, earthquake and tsumani

This was originally posted in March 2011, and is being reposted in commemoration of this terrible tragedy.

Thoughts on the Sendai, Japan, earthquake and tsunami

I used to live in Japan and experienced my first earthquakes while I was there. The good thing about that is that I know that Japanese construction codes and building practices require that buildings there, large and small, are good at shaking without failing when the earth shakes.

The earthquake that shook that country last Friday (9.0 on the Richter scale - two magnitudes more powerful than the 6.9 magnitude Loma Prieta earthquake that hit the San Francisco/Santa Cruz area in 1989) pushed the country right to the edge of its limits, and in some cases beyond. The Sendai earthquake's epicenter was about 80 miles east of northern Honshu Island and at a depth of about 24 miles. Fortunately we have heard no reports of large buildings collapsing, though there are confirmed reports that some skyscrapers swung as much as 20' from side to side during the quake. Unfortunately, however, the quake triggered a massive tsunami.

There have been more than 150 aftershocks over a very large region. The map below shows the locations and relative strengths of aftershocks (so far).

Sadly, NPR reported this morning that the death toll from the earthquake and devastating tsunami that followed is now estimated to be around 10,000.

Scientists have reported that this earthquake was so powerful and that the slippage significant enough that stationary GPS reference location points in Japan shifted 8 feet (2.4 meters) - that's right, the entire country shifted 8 feet. Scientists also discovered that the angle of the axis of the earth shifted by about 4" (10 cm).

The resulting tsnuami waves devastated the northeast coast of Japan's main island of Honshu, striking near the large, coastal city of Sendai. The main tsunami wave that struck there was 23 feet (7 meters) tall. The size and force of that wave caused it to smash through low-lying coastal regions, destroying structures, farms, and killing ~19,000 people. This image from NOAA (The National Oceanographic and Atmospheric Administration) shows the wave height of the Sendai earthquake tsunami as it moved across the Pacific Ocean.

If that's not enough, some nuclear power plants in Japan suffered damage, and there are justified concerns that reactors are leaking radioactive materials. Recent reports state that over 180,000 people have been evacuated from areas where damaged reactors are located. One reactor has suffered two massive explosions, and there are further concerns about the possibility of core melt-downs.

My heart goes out to the people of Japan in these times of terrible natural disasters.